This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-128095 filed on Apr. 30, 2002.
1. Field of the Invention
The present invention generally relates to an ignition coil device for an engine of, for example, an automobile and more specifically to an ignition coil assembly that includes a plurality of ignition coils, which are connected to corresponding spark plugs securely installed in plug holes of the engine.
2. Description of Related Art
For example, Japanese Unexamined Patent Publication No. 9-250437 discloses an integrated connector block, in which connectors for supplying electricity to corresponding ignition coils are integrated. The integrated connector block includes a connector block main body, which is formed as an elongated body made of a resin material. Coil connectors are integrally formed in a lower surface of the connector block main body. Each ignition coil, which is secured to a corresponding spark plug installed in an engine, is installed to and is thus engaged with a corresponding one of the coil connectors in an axial direction of the corresponding ignition coil, i.e., in an axial direction of the corresponding spark plug.
Furthermore, in order to allow installation of the ignition coils to the plug holes of the engine in a single step, an ignition coil assembly, which includes a plurality of ignition coils arranged at predetermined intervals, has been proposed. For example, as shown in FIG. 7, one such ignition coil assembly 21 includes a resin base member 13 that holds a plurality of ignition coils 12 at corresponding positions, which correspond to positions of plug holes 131 of an engine 130. Each ignition coil 12 may be threadably secured to the base member 13 through use of a bolt. Alternatively, each ignition coil 12 and the base member 13 may be integrally molded using a resin material. In either way, each ignition coil 12 and the base member 13 are integrated together. Thereafter, the ignition coil assembly 21 is installed to the engine 130 by axially installing the ignition coils 12 into the corresponding plug holes 131, and longitudinal ends of the base member 13 are secured to the engine 130 by bolts 13c. 
In the previously proposed ignition coil assembly 21, all of the ignition coils 12 need to be simultaneously removed from the corresponding plug holes 131 of the engine 130 when one or more spark plugs need to be examined or replaced. This results in difficult work. That is, each ignition coil 12 is connected to the corresponding one of the spark plugs through a plug cap 12d. When all of the ignition coils 12 are simultaneously removed from the corresponding plug holes 131, the force required to remove all of the ignition coils 12 is equal to the product of the force for removing one ignition coil 12 multiplied by a number of the ignition coils 12. Thus, the removal operation of the ignition coils 12 becomes difficult, and, in some cases, it is impossible to remove the ignition coils 12.
The present invention addresses the above disadvantage. Thus, it is an objective of the present invention to provide an ignition coil assembly, which has a structure that allows easy removal of a base member from each ignition coil to allow easy maintenance work.
To achieve the objective of the present invention, there is provided an ignition coil assembly for an engine. The engine includes a plurality of plug holes, each of which receives a corresponding one of a plurality of spark plugs. The ignition coil assembly includes a plurality of ignition coils and a base member. The ignition coils are arranged to be electrically connected to the spark plugs, respectively. The base member detachably engages and holds the ignition coils at corresponding positions, which correspond to positions of the plug holes of the engine. Disengaging force for disengaging each ignition coil and the base member from each other is set to be smaller than disengaging force for disengaging each ignition coil and the corresponding one of the spark plugs from each other.